As a major provider for the cracking activity of a heavy oil cracking catalyst, Y-type molecular sieve having a high cracking activity and a high activity stability has been always a core technical problem of the research in the field of catalysis. Catalytic cracking process is an important process for lightweight conversion of heavy oil, also is one of the main sources for the benefits of each refinery.
In recent years, in order to improve the yield of light oil, a number of researches have been conducted by the related research institutes at home and abroad on how to improve the cracking activity and activity stability of Y-type molecular sieve. Current industrial modification methods mostly use a modified Y-type molecular sieve by rare earth ion exchange, combined with the optimization of the calcination condition to allow the rare earth ions to migrate to the sodalite cage as many as possible to inhibit the molecular sieve framework from dealumination, thereby improving the structural stability and activity stability of the molecular sieve, and achieving the object of improving the heavy oil conversion activity and selectivity of the catalyst.
To further enhance the catalytic properties of ultrastable REY molecular sieve, there have been proposed a method of phosphorus modification in relevant literatures.
CN1353086A discloses a method for preparing a Y-type molecular sieve containing phosphorus and rare earth, wherein the resultant Y-type molecular sieve cars significantly reduce the olefin content in FCC gasoline, while maintaining good coke selectivity. The method includes firstly mixing the NaY molecular sieve with ammonium ions and rare earth ions for exchange and subjecting it to a hydrothermal calcination, and then reacting it with a phosphorus compound to incorporate 0.2 to 10 wt % (in terms of P2O5) of phosphorus, followed by a hydrothermal calcination.
CN1330981A discloses a phosphorus-containing Y-type zeolite and a preparation method thereof. Said phosphorus-containing Y-type zeolite contains, in addition to phosphorus, a silicon component and a rare earth component wherein the silicon component is loaded by impregnating the zeolite with a solution of silicon compound; the content of the silicon component is 1-15 wt % in terms of SiO2; the content of the phosphorus component is 0.1-15 wt % in terms of P2O5; and the content of the rare earth component is 0.2-15 wt % in terms of a rare earth oxide. The molecular sieve is obtained by co-impregnating the rare earth-containing Y-type zeolite with a solution containing silicon and phosphorus, drying and then hydrothermal calcination at 550-850° C. The phosphorus-containing Y-type zeolite has a high crystallinity and a good catalytic performance after hydrothermal treatment, while a cracking catalyst of the phosphorus-containing Y-type zeolite has a strong heavy oil conversion capacity and a good product distribution.
CN1325940A discloses a phosphorus-containing catalyst for cracking hydrocarbons and a preparation method thereof. The catalyst is composed of 10-60 wt % of Y-type molecular sieve or Y-type molecular sieve with MFI structure molecular sieve and/or β-molecular sieve, 0-75 wt % clay, 10-60 wt % of two types of alumina, 0.1-7.0 wt % of phosphorus in terms of P2O5, and 0-20 wt % of rare earth in terms of RE2O3. The catalyst is obtained by mixing the molecular sieve treated with a phosphorus-containing solution, optimally the molecular sieve untreated with the phosphorus-containing solution, with clay and double aluminum binder, calcinating at 500° C. or spray drying, and then treating with a phosphorus-containing solution. The catalyst may reduce the olefin content in the product gasoline fraction to 20-26 wt %.
CN1317517A discloses a FCC catalyst for reducing olefin content in gasoline and a preparation method thereof. The catalyst is composed of zeolite-type active component, amorphous silicon aluminum oxide and kaolin, wherein the active component is consisting of 0.5-5% (a percentage by weight relative to the FCC catalyst, the same applies hereinafter) ZSM-5, 0.5-15% RE Y-type zeolite, 20-40% phosphorus and RE composite-modified ultrastable Y-type zeolite. The phosphorus and RE composite-modified ultrastable Y-type zeolite is obtained by subjecting Na Y zeolite to mixing with RE and ammonium salt for exchange, and a hydrothermal calcination treatment, followed by a reaction with phosphorus compound, and a second calcination treatment, wherein the weight ratio of RE2O3/Y-type zeolite is 0.02-0.18, the weight ratio of ammonium salt/Y-type zeolite is 0.1-1.0, the weight ratio of P/Y-type zeolite is 0.003-0.05, the calcination temperature is 250-750° C., the steam condition is 5-100%, the duration is 0.2-3.5 hours, and the resultant zeolite has a rare earth content of 2-12%, a unit cell constant of 24.45-24.46 nm, and a phosphorus content of 0.2-3% (in terms of P). As compared with conventional catalysts, this catalyst can significantly reduce the olefin content in gasoline, while ensuring the distribution of other products and the octane number of gasoline essentially unchanged.
CN1217231A discloses a phosphorous-containing faujasite catalyst for cracking hydrocarbons and a preparation method thereof. The catalyst comprises 10-60 wt % of faujasite, 0.01-1.5 wt % of phosphorus, 0.1-40 wt % of RE oxide, 10-60 wt % of aluminum binder (in terms of aluminum oxide), and 0-75 wt % of clay, wherein the aluminum binder is from pseudo-boehmite and alumina sol respectively. The phosphorus-containing faujasite is prepared by mixing faujasite with an aqueous solution of a phosphorus-containing compound uniformly, standing for 0-8 hours, drying and calcinating at 450-600° C. for 0.5 hour or more.
None of the phosphorus modification methods for RE Y-type molecular sieve provided in the above patent documents specifies the precise localization of rare earth ions and the dispersability of the molecular sieve. However, in the ultrastable RE Y-type molecular sieve containing phosphorus and rare earth involved in this invention, the rare earth ions could be precisely located in sodalite cages, and it is characterized by improving both particle dispersability and light oil yield due to the incorporation of a dispersant and a phosphorus-containing compound.